Wireless systems in the cellular context are currently being implemented using fourth generation (4G) standards. These 4G standards include Long Term Evolution (LTE) standards developed by the 3G Partnership Project (3GPP). LTE cellular systems make use of an Internet protocol (IP) based packet core referred to as Evolved Packet Core (EPC). The EPC interconnects multiple base stations within the system. A given base station, which may also be referred to as a Node B, or more particularly an evolved Node B (eNB), communicates over an air interface with multiple user terminals. Individual user terminals are also referred to as user equipment (UE).
The air interface between an eNB and UE in an LTE cellular system includes a variety of uplink and downlink channels. See, for example, 3GPP TS 36.211, V9.1.0, 3rd Generation Partnership Project Technical Specification, Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA), Physical Channels and Modulation (Release 9), March 2010, which is incorporated by reference herein.
In order to support high-speed communications over such uplink and downlink channels, LTE cellular systems and other types of wireless systems often require a highly accurate clock. For example, in LTE Node B applications, the specified clock timing accuracy requirement is about 50 parts per billion (ppb) for frequency accuracy and about 3-10 milliseconds (ms) for phase accuracy. In order to meet this strict clock timing accuracy requirement, each Node B generally must incorporate Global Positioning System (GPS) functionality. However, such arrangements can unduly increase the cost, complexity and power consumption of the Node B. Similar issues arise in other wireless system base stations that rely upon GPS functionality in order to meet their clock timing accuracy requirements.